This invention generally relates to a method and apparatus for purification of air, and more specifically to a method and apparatus for removing odoriferous substances from air by ozone oxidation and additionally treating the remaining mixture to eliminate the ozone molecules therefrom.
Odor may be controlled by the following methods: ventilation, combustion, masking and counteraction, destruction by chemical reactions, and removal by sorption and chemisorption.
Open windows have long been the symbol of wholesome indoor living quarters. The method involved -- ventilation -- is one of the simplest methods of air purification and consists basically in bringing odorous gasses or vapors below a threshhold limit or in certain cases below odor limits at which the human nose can sense. However, ventilation becomes uneconomical in January and other midwinter months when heating must be provided.
Combustion is most expensive of the methods, and consists of oxidizing or burning at high temperatures the hydrocarbons or organic compounds that most odorous vapors consist of, converting them to CO.sub.2 and water vapor. In certain cases, the burning of sulfur and nitrogen containing compounds merely convert them to new oxides that have a higher tolerability limit than the parent compound, and thus are less objectionable. However, due to the fact that combustion normally takes place at 1200.degree. to 1400.degree.F in incinerators and afterburners, and at 500.degree.-800.degree.F with the aid of catalysts, combustion becomes practical only in certain instances. For example, combustion may be practical when effluent gasses are well above the ambient temperatures. Also, when waste heat can be economically used for process heating or returned to fuel system for economy. Further, when the odorants have not economical value and can contribute to heat or combustion.
A further disadvantage of combustion is that it must generally be complete. Incomplete combustion or partial oxidation of some organic compounds produces intermediate oxidation products such as Aldehydes and organic acids that are worse odor offenders.
Masking consists of adding more pleasant odorants to overcome the concentration of existing bad odors. It also can mean adding an anasthetic substances to depress the senses of smell. In this manner, the bad odor is less objectionable. Masking can also be done by blending several odors to diminish the intensity of the original one. Generally, masking involves the blending of two or more odors so that the total odor is increased but is more acceptable.
Counteraction is a method which consists of introducing two antagonistic odors so that when sniffed together, both odors can be diminished or even totally eliminated. Benzene, Toluene, Zylene, and Durene fall into this catagory. In counteraction, the total odor is decreased in intensity, where in masking it is increased in intensity. The disadvantage of both of these methods is that they are highly specialized fields, especially counteraction, and are not easily controlled.
Air borne can be destroyed by a great number of gas, gas-solid or gas-liquid chemical reactions. Two types of chemical groups exist, namely those that are specified reagents for specific contaminants, such as ammonia and acedic acid, and those with broad spectrum reagents for a broad range of contaminants, such as ozone and chlorine. In the use of such chemical reagents, great care must be taken since these reagents may be toxic, corrosive, irritating or odorous, or can produce end products with such properties.
Removal of odoriferous substances may also be achieved by adsorption, wherein adhesion of molecules of gasses takes place to the surface of solid bodies. Absorption depends on surface area and can become uneconomical when large quantities of air are to be treated. The same observation applies to chemabsorption. When a sorbate enters into chemical reaction with a sorbent, the bond is very strong and difficult and sometimes impossible to reverse. When two or more sorbates enter into chemical reaction by virtue of their proximity and condensed conditions in the sorbent state, this type of chemabsorption is also called "surface catalysis". The initial capital investment as well as maintainence costs in the use of these two methods is high.
Based on the above review of the existing methods of air purification, it becomes readily clear that no one method can do a complete job of eliminating odors from the air in an economical fashion.
Ozone, which is one of the most powerful oxidizing agents readily available to man, has a life span, although unstable, to make it live long enough to become objectionable to suburban communities. Yet, ozone is still the cheapest and one of the most effective oxidizers available.
Activated carbon is a well known adsorbant and can eliminate odors but works poorly on low concentrations. Another disadvantage of activated carbon is that used alone it cannot remove all odors from the air. The principle of the gas mask has been employed in many instances to eliminate odors and noxious vapors from living and working spaces. Such use have gained momentum in recent years with the introduction of air conditioning. The traditional method of removing odors and correcting a stale and vitiated atmosphere in living quarters is by ventilation with fresh air from outside. As suggested above, the admission of large quantities of outside air, however, can increase the cost of air conditioning to a prohibitive level.
In many situations, therefore, it has become a more general practice to recirculate much of the air and maintain the purity and freshness by passing the air continuously through a bed of granular activated carbon. As suggested above, however, this approach is not suitable, from a practical and economical point of view, where very intense or low concentrations of odoriferous substances are to be removed from air.
The present invention is for a method and apparatus for treating contaminated air efficiently and economically with an effectiveness not achievable with any of the above enumerated methods of purification. Both the initial capital expense, as well as the operation of the device of the present invention is substantially less than that of comparable devices known in the art. A further advantage of the present invention is that the treated air is substantially free of the odoriferous substances as well as free from any additional odors or chemicals which are generated during the treatment process.